Various stents are known in the art. Typically, stents are generally tubular in shape, and are expandable from a relatively small, unexpanded diameter to a larger, expanded diameter. For implantation, the stent is typically mounted on the end of a catheter with the stent being held on the catheter in its relatively small, unexpanded diameter. Using a catheter, the unexpanded stent is directed through the lumen to the intended implantation site. Once the stent is at the intended implantation site, it is expanded, typically either by a balloon or by allowing the stent to self-expand. In either case, the expanded stent resists the tendency of the vessel to narrow, thereby maintaining the vessel's patency.
Stents may be constructed from tubes or from a flat sheet of metal, which is rolled and fixed such as by welding, mechanical lock or otherwise, to form the tubular structure of the stent.
Some examples of patents relating to stent designs include U.S. Pat. No. 4,733,665 to Palmaz; U.S. Pat. Nos. 4,800,882 and 5,282,824 to Gianturco; U.S. Pat. Nos. 4,856,516 and 5,116,365 to Hillstead; U.S. Pat. Nos. 4,886,062 and 4,969,458 to Wiktor; U.S. Pat. No. 5,019,090 to Pinchuk; U.S. Pat. No. 5,102,417 to Palmaz and Schatz; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 5,161,547 to Tower; U.S. Pat. No. 5,383,892 to Cardon et al.; U.S. Pat. No. 5,449,373 to Pinchasik et al.; and U.S. Pat. No. 5,733,303 to Israel et al.
One type of stent is known as the helical or coiled stent. Such stent designs are described in, for example, U.S. Pat. Nos. 6,503,270 and 6,355,059, incorporated herein, in toto, by reference. This stent design is configured as a helical stent in which the coil is formed from a wound strip of cells wherein the cells form a serpentine pattern comprising a series of bends. Other similar helically coiled stent structures are known in the art.
Prior stent designs have focused on providing sufficient radial strength when it is expanded so that it can sufficiently support the lumen. Stents with high radial strength, however, tend also to be more longitudinally stiff than the vessel in which it is implanted. When the stent is more longitudinally stiff than the vessel in which it is implanted, increased trauma to the vessel may occur at the ends of the stent, due to stress concentrations on account of the mismatch in compliance between the stented and un-stented sections of the vessel, or otherwise. In addition, the stent may interfere with the vessel's natural tendency to bend and to stretch. Conversely, stents with good flexibility often lack sufficient and/or uniform radial support for the vessel wall. Thus, a continued need exists in the art for a stent having a balance of good radial strength and a high degree of longitudinal flexibility.
Another problem in the art arises when trying to simplify the manufacturing process of a stent to reduce costs yet prevent manufacturing defects, while still producing a stent with uniformly high flexibility and sufficient radial support.